1. Technical Field
The invention relates to dispensing equipment and in particular to a dispensing device for dispensing flowable materials such as resins, epoxies, etc. in a positively controlled manner. More particularly, the invention relates to a dispensing device for dispensing small amounts of a flowable material in an accurate, repeatable, positive manner.
2. Background Information
Various dispensers have been developed for the deposition in small accurately controlled shot applications of a flowable material, such as adhesives, sealants, lubricants or the like. Although it is relatively easy to dispense individual shots of such material, it becomes increasingly difficult when the amount dispensed is an extremely small shot size, for example, 0.001 cc and smaller, especially when the various materials being dispensed have a wide range of viscosities. Heretofore, many such dispensing devices and mechanisms use a spring biased check valve. However, it is difficult to accurately control the flowable material or liquid being dispensed, especially when in a very small shot application, with such spring-biased valves due to the inability to accurately control and maintain the spring rate. It is furthermore necessary that when dispensing such small shot sizes of material that the fluid flow be dripless.
One known dispensing device is shown in U.S. Pat. No. 4,095,722 which involves filling a portion of a tube with material and then isolating a portion of the material to be dispensed by pinching off sections of a tube containing the material for subsequently dispensing to ensure that only the amount of material in the pinched off area is dispensed.
Various types of positive displacement devices and systems using this pinch-off tube concept for dispensing a single shot of material was distributed by former SCM Metal Products, Inc. of Indianapolis, Ind., under the trademark SCM/DISPENSIT. Another type of system for dispensing a single shot or drop of fluid was also distributed by SCM Metal Products, Inc., and identified as its 1000 Series positive displacement dispenser.
Although these prior art small shot or drop dispensers are satisfactory for many applications, it is desirable to provide an improved dispenser for dispensing small shots of a flowable material in a positive manner, which is dripless, and which operates with continual repeatable accuracy despite changing viscosities and types of materials, and which will accommodate a wide range of material viscosities, reduces maintenance and changeover costs, eliminates post dispensing drippage, and provides an efficient and dependable device for dispensing such small shots of a flowable material.